Many oil field tubular connections are threaded together (makeup) and unthreaded (broken apart) using a power tong and a backup tong. The backup tong is fixed to the lower stationary joint of pipe, while the upper pipe is rotated by actuating the power tong to makeup or break apart the threaded connection. As oilfield tubular connections become more sophisticated, increased emphasis must be placed on reliably making up each seal within the connection, whether metal-to-metal or elastomeric. Over-torquing a threaded connection is also a problem, particularly when using more expensive tubulars which may include chrome or other chemically resistive coatings. An oilfield tubular connection makeup at its proper torque value is thus becoming increasingly important. Accurate makeup torque readings are frequently not obtained with prior art equipment, particularly for fiberglass or other non-ferrous tubulars which typically have a desired low makeup torque.
A backup tong may be "tied off" by connecting a cable between the tong body and any stationary member on the rig. The generally heavier power tong may be supported from a vertical cable or lifting sling, and may include a spring for raising and lowering the power tong relatively short distances. A separate cable may be used to tie off the power tong to prevent rotation of the power tong body. The power tong and backup tong thus are supported independently of each other. This arrangement allows for pivoting of the tubulars and sideloading on the connection threads, which is detrimental to reliable makeup of the connection. A makeup torque indicator may be provided in the cable which ties off the power tong, and the angle of the cable relative to the tong affects the torque measurement. Also, the torque applied to the connection cannot be easily measured due to the high sideloading caused by pipe twisting.
Another arrangement for supporting a power tong and a backup tong includes a vertical cable or lifting sling as described above with an optional spring for vertically raising and lowering the power tong short distances. The backup tong is supported by the power tong, typically from a frame which includes a plurality of legs which extend downwardly from the power tong and through apertures in the backup tong. Once activated to engage the lower pipe, the position of the lower backup tong is fixed. A plurality of leg springs may be used for allowing limited vertical movement of the power tong with respect to the fixed backup tong during makeup and breakout of the threaded connection. A rigid torque plate typically extends downwardly from the power tong and engages a load cell provided on the backup tong for measuring torque. The torque plate thus slides along the load cell as the connection is made up. This arrangement also tends to allow for misalignment and twisting of the pipe, thereby creating sideloading and inaccurate torque readings. Since the load cell is in a different vertical plane than the power tong, pipe and tong twisting results in inaccurate torque measurements.
In yet another arrangement, the backup tong is supported from the power tong with a frame as described above, and a separate tong support plate provided below the backup tong is also suspended from the power tong. As in the previously described arrangement, the backup tong is firmly fixed to the lower joint of pipe, and will not move vertically or horizontally during makeup of the threaded connection. The power tong and the support plate thus move vertically with respect to the fixed backup tong during the makeup and breakout operations. The power tong, the support plate, and the frame also move horizontally relative to the fixed backup. The combined weight of these components moving horizontally can affect the accuracy of the torque reading, particularly at low torques. The output from the load cell has questionable accuracy because the load cell is provided within the plane of the backup tong, and the power tong twists relative to the fixed backup tong. None of these designs thus overcome the problem of side and axial thread loading, and inaccurate torque readings. For each of these arrangements, pipe twisting results in thread sideloading which adversely effects the reliability of the threaded connection.
Single joint compensators have been used for installation between a tubular string and an elevator to assist in the stabbing and makeup of threaded connections for oilfield tubulars. The single joint compensator provides weight balancing and compensation, and may include an air spring with suitable lifting and stroking capability, along with an adjustable spring. Although single joint compensators have been used in some applications to minimize the galling of threads and to reduce the difficulties associated with initially stabbing the connection, these compensators have not overcome the problems discussed above with respect to horizontal and vertical sideloading on threaded oil field tubular connections, and with respect to inaccurate torque measurements.
The disadvantages of the prior art are overcome by the present invention. An improved support and method are hereinafter provided for interconnecting both a power tong and a backup tong in a manner which will improve the reliability of the threaded oilfield tubular connection by reducing sideloading and improving torque measurement reliability.